Investigations On The Combustion Kinetics Of Furan-series Biomass Fuels

Energy depletion and environment degradation are two major challenges facing the world today.As a kind of renewable energy,biomass fuel has unique advantages in alleviating energy shortage,ensuring energy security,and protecting the environment.Furan biomass fuel,as the representative of the second generation biomass fuel,has similar physical and chemical properties to those of gasoline,and may be directly used in the existing internal combustion engines as a substitute fuel of gasoline or octane number enhancer for gasoline.With the development of synthetic methods for converting biomass into furan biofuels,furan fuels have attracted more and more attention.Their combustion kinetics are one of the hotspots in current combustion research.This thesis focuses on the effect of the branched chain structure of furan fuels on their combustion characteristics,including 2-ethylfuran,2-acetylfuran and methyl2-furoate.The main research work is briefly described as follows.（1）Pyrolysis experiments of 2-ethylfuran at different pressures and low-temperature oxidation experiments of 2-ethylfuran at different equivalence ratios under atmospheric pressure were carried out in a flow tube reactor and a jet stirred reactor（JSR）,respectively,and the reactants,intermediates,isomers and products during the pyrolysis and oxidation experiments were identified and measured by synchrotron vacuum ultraviolet photoionization mass spectrometry（SVUV-PIMS）.The identification and measurement of reactants,intermediate species,isomers and products during the pyrolysis and oxidation experiments were carried out using SVUV-PIMS.The laminar burning velocity of2-ethylfuran were measured at initial temperatures of 373,403 and 433 K,initial pressures of 1,2 and 4 bar,and equivalence ratios of 0.7-1.4,based on the constant volume bomb experimental setup,combined with the high-speed schlieren imaging system and a temperature-pressure control system..A large number of intermediate species and products were identified and measured in the pyrolysis and oxidation experiments of 2-ethylfuran.The potential energy surface for the single-molecule dissociation of 2-ethylfuran was constructed at the CBS-QB3 level,and the temperature-and pressure-dependent rate constants for the reactions associated with the potential energy surface were calculated based on the transition state theory and the Rice-Ramsperger-Kassel-Marcus theory as well as the Eckart tunneling effect correction to solve the master equation.The 2-ethylfuran pyrolysis model was updated and refined based on the 2,5-dimethylfuran model and validated against the current experimental results,which showed that the current model can reproduce well the results of most experimental species and reproduce the trend of the laminar combustion rate of 2-ethylfuran flames.Furthermore,experimental results show that2-ethylfuran has no negative-temperature-coefficient zone.（2）The experiments on the atmospheric pressure pyrolysis of 2-acetylfuran were carried out by SVUV-PIMS combined with gas chromatography in the JSR.Several important pyrolysis intermediates and products,such as acetylene,ethylene,carbon monoxide,ketene,vinyl acetylene,cyclopentadiene,2-methylfuran,ethynyl vinyl ketone and furfural,etc.,and isomers such as allene/propyne,furan/vinyl ketene,benzene/fulvene,etc.,were identified and measured.The potential energy surface of the unimolecular dissociation reaction of 2-acetylfuran was constructed at the CBS-QB3 level.Based on the transition state theory and Rice-Ramsperger-Kassel-Marcus theory and the Eckart tunnel effect correction,the main reaction equation was solved,and the temperature-and pressure-dependent rate constants of the relevant reactions on the potential energy surface were calculated.A pyrolysis model of 2-acetylfuran was developed based on the 2-methylfuran combustion model and validated against the current experimental results.The results show that the current model reproduces the experimental results well for most species.In addition,the contributions of ipso-substitution reactions by CH₃ and H to the consumption of2-acetylfuran were also compared.（3）The potential energy surface for the reaction of methyl 2-furoate+hydroxyl was constructed at the CCSD（T）/CBS//M06-2X/cc-p VTZ level.The reactions of isomerization and decomposition into primary radicals after OH-addition were also determined.The temperature-and pressure-dependent rate constants for the relevant reactions on the potential energy surface were calculated based on transition state theory and the Rice-Ramsperger-Kassel-Marcus theory and the Eckart tunnel effect correction to solve the master equation.The results show that the H-abstraction reaction at the CH₃ on the branched chain and the OH-addition reaction at the C（2）and C（5）on the furan ring are the main reaction channels in the reaction system.（4）The effects of molecular structure of furan series fuels such as2-methylfuran,2-ethylfuran,2-acetylfuran,2,5-dimethylfuran,and methyl2-furoate on the reactivity of pyrolysis and the generation of carbon soot precursors were compared by experiments and numerical simulations at atmospheric pressure.The results showed that 2-methylfuran had the weakest pyrolytic reactivity,2-ethylfuran had the strongest reactivity,and 2-acetylfuran had a low tendency to produce carbon soot precursors.